The invention relates to a memory architecture.
A digital image may be processed by a digital imaging system to, as examples, enhance the image or compress the amount of data that is associated with the image. Unfortunately, the processing may include numerous memory interactions which may consume a considerable amount of time and thus, depending on the application, may reduce the benefits of the processing. For example, a digital imaging system may compress data associated with a digital image to reduce the amount of redundant and/or nonessential information. This compression may be beneficial, for example, for purposes of transmitting the data, as a smaller amount of data may be transmitted more quickly. For a digital camera, the compression may also be beneficial, for example, for purposes of storing the data in a flash memory of the camera, as more frames may be stored in the memory. However, the compression may itself consume a considerable amount of time which reduces the benefits gained by the compression.
For example, referring to FIG. 1, a digital imaging system 5 may include a digital camera 12 that electrically captures a digitized representation (called a pixel image) of an optical image 11. The pixel image typically is represented by a frame of data that is initially stored in a memory 10 of the camera 12, and portions, or pixels, of the image are represented by one or more bytes of the frame. Although the camera 12 may transmit (via a serial bus 15, for example) the original, uncompressed frame to a computer 14 (for further processing and for displaying the pixel image, as examples), the camera 12 might compress the frame before transmission. However, the time required to compress the frame adds to the camera's total image processing time and thus, may affect the maximum speed at which the camera 12 takes successive snapshots.
The camera 12 could possibly use either a one-dimensional (1-D) or a two-dimensional (2-D) frame-based compression technique to compress the frame. In 1-D compression, the camera 12 might operate on the original pixel image in either a horizontal or a vertical direction. In this manner, the camera 12 either operates in a vertical direction along the pixel image in row order to compress the data associated with each row of the image or operates in a horizontal direction along the pixel image in column order to compress the data associated with each column of the pixel image. However, to obtain a better compression ratio, the camera 12 might use the 2-D compression, a technique which typically consumes substantially more time, as described below.
Wavelet compression may use 2-D compression. In this manner, the original pixel image is initially transformed into smaller spatial frequency sub-band images, each of which represent the pixel image after being spatially filtered, as described below. The data that indicates the frequency sub-band images is compressed to form the compressed frame.
The transformation of the original pixel image into the frequency sub-band images typically includes spatially filtering the original pixel image in both the vertical and horizontal directions. For example, referring to FIG. 2, to generate four frequency sub-band images 19 (each having a resolution of 640 columns by 480 rows, for example), an original pixel image 18 (having a resolution of 1280 columns by 960 rows, for example) is processed along a vertical direction of the pixel image in row order. In this processing, both high spatial frequency transitions and low spatial frequency transitions are filtered out to produce two intermediate sub-band images 18a and 18b (each having a resolution of 1280 rows by 480 columns): one image 18a formed from the low pass filtering and the other image 18b formed from the high pass filtering. The intermediate sub-band images 18a and 18b, in turn, are processed along a horizontal direction of the pixel image in column order. In this processing, both low and high spatial frequency transitions are filtered out to produce the four frequency sub-band images 19a, 19b, 19c and 19d.
The sub-band image 19a may be denoted an "LH" sub-band image, where the "L" denotes low pass filtering along the vertical direction, and the "H" denotes high pass filtering along the horizontal direction. Similarly, the images 19b, 19c and 19d may be denoted by the letters, HL (to indicate high pass filtering along the vertical direction and low pass filtering along the horizontal direction, for example), HH and LL, respectively. The data associated with each frequency sub-band image 19 is compressed to form the resultant compressed frame.
Thus, because 2-D compression operates along both the horizontal and vertical directions of the image, 2-D compression typically requires substantially more interactions with a memory and thus, typically consumes more clock cycles than 1-D compression. As a result, although 2-D compression generally produces a better compression ratio, 2-D compression may require substantially more time. Because slow compression times may minimize the snapshot-to-snapshot performance of the camera, digital cameras typically do not use 2-D compression.
Thus, there is a continuing need for a digital imaging system that reduces the time required for two-dimensional processes.